Effect of Photogenerated Dipoles in the Hole Transport Layer on Photovoltaic Performance of Organic–Inorganic Perovskite Solar Cells

Abstract

to the electronic and morphological parameters in the active perovskite layer, the electron transport layer (ETL) and hole transport layer (HTL) are significantly important in determining the photovoltaic performance in perovskite solar cells. [3][4][5][6] Specifically, the role of a transport layer in solar cells is to facilitate charge transport and assist charge collection toward the respective electrodes as well as inhibiting from recombination of charge carriers on the path to the electrodes. [3] Meanwhile, the open circuit voltage (V oc ) is normally determined by the energy differences between the Fermi levels of the ETL and the HTL. There are certain prerequisites for a hole transport material in order to perform more efficiently in perovskite solar cells, such as energy band alignment, suitable hole mobility, chemical compatibility with the perovskite layer as well as good thermal and photochemical stability. [5,6] In addition, morphology and crystallinity of this layer plays an important role. The importance and influence of these parameters in the transport layer on perovskite solar cells performance have been extensively investigated. [3,[5][6][7][8][9][10] In this article, we demonstrate the importance of photogenerated dipoles in the HTL as a new strategy to improve the photovoltaic performance of planar perovskite solar cells. In order to explore this effect, we select two HTLs with similar conjugated thiophene backbones, namely PTB7 and P3HT with significant and negligible optically generated dipoles. Moreover, our measurements based on space charge limited current model indicate that PTB7 and P3HT have hole mobilities in the same order in agreement with previous publications (Figure S1, Supporting Information). [11][12][13][14] It has been shown that PTB7 has a relatively large internal dipoles through intrachain charge transfer from benzodithiophene to thienothiophene moieties under photoexcitation. [15] The dipole moments (D) in ground and excite states have been measured to be 3.76 and 7.13 for PTB7 and 0.19 and 0.43 for P3HT, respectively. [15] In general, perovskites have the advantage of both bulk polarization and semiconducting properties. [16][17][18][19][20] It was shown that the presence of a polar molecule, methylammonium at the center of perovskite introduces the possibility of orientational P3HT-poly(3-hexylthiophene) are separately used as the HTL with significant and negligible photoinduced dipoles, respectively. Electric field-induced photoluminescence quenching provides the first-hand evidence to indicate that the photoinduced dipoles are partially aligned in the amorphous PTB7 layer under the influence of device built-in field. By monitoring the recombination process through magneto-photocurrent measurements under device operation condition, it is shown that the photoinduced dipoles in PTB7 layer can decrease the recombination of photogenerated carriers in the active layer in perovskite solar cells. Furthermore, the capacitance measurements suggest that the photoinduced dipoles ...

Charge Injection, Carriers Recombination and HOMO Energy Level Relationship in Perovskite Solar Cells

“…Regarding polymer based cells, in this study we have surpassed the reported power conversion efficiency (PCE) record for PCPDTBT acting as HTM 20 , while for P3HT and PTB7, the efficiencies obtained are similar to the best efficiencies reported avoiding the use of dopants 31, 32 .…”

Improved Processability and Efficiency of Colloidal Quantum Dot Solar Cells Based on Organic Hole Transport Layers

“…[49,50] Enhanced charge separation by the photoinduced internal dipoles of PTB7 has been demonstrated in organic photovoltaics. [49,50] Enhanced charge separation by the photoinduced internal dipoles of PTB7 has been demonstrated in organic photovoltaics.…”

“…[49] More recently, improvement in the charge extraction of perovskite solar cells by the photogenerated dipole effect of PTB7 as a Adv. [50] The photoinduced alignment of dipoles in PTB7 reduced the charge accumulation and recombination at the perovskite/PTB7 interfaces. 2018, 8, 1800572 HTL was reported.…”

“…2018, 8, 1800572 HTL was reported. [50] It is known that the degree of V peak shift in reverse bias with respect to illumination intensity reflects the degree of interfacial charge accumulation. While the effects of interfacial dipoles at ETL/CQD interfaces are relatively well documented, [8,16,17] photoinduced dipole effects of polymer HTLs in CQDPVs have never been reported.…”

Long‐Lasting Nanophosphors Applied to UV‐Resistant and Energy Storage Perovskite Solar Cells

“…[1] Benefiting from these excellent properties, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has greatly improved to converted light by photoactive materials. [1] Benefiting from these excellent properties, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has greatly improved to converted light by photoactive materials.…”